Post-Grenfell research has transformed our understanding of external fire spread. We review the latest findings from BRE, DCLG, and international research programmes.. The Knowledge Gap Before Grenfell, our understanding of external fire spread was largely based on BS 8414 large scale tests and limited fire incident data. Post 2017 research has dramatically expanded our knowledge. Key Research Findings BRE External Fire Spread Programme Cavity barriers are critical — missing or misaligned barriers enable rapid fire spread Combustible insulation behind non combustible rainscreen can still allow fire spread through the cavity Window design and fire stopping at floor edges are critical control points DCLG Desktop Study Review Desktop studies cannot reliably predict external wall fire performance Full scale testing (BS 8414) is the only reliable method Even BS 8414 has limitations — it tests a single configuration International Research Australian research on aluminium composite panels confirms rapid flame spread above 400°C Swedish research on ventilated facades shows cavity ventilation accelerates fire growth Canadian research on fire barriers demonstrates importance of installation quality Design Implications 1. Full scale testing should be the default for novel external wall systems 2. Cavity barriers must be installed by competent persons with third party inspection 3. Combustible materials should be avoided wherever possible, even behind non combustible faces 4. Maintenance of external wall fire safety features must be planned and documented For external wall fire safety advice, contact Magnus Opifex.